In precision machining of a discoid workpiece such as a semiconductor wafer, there has been conventionally a grinding method called double-disc grinding to grind both surfaces at the same time. In the double-disc grinding, a cup-type wheel is generally used as a grinding wheel, and it has a plurality of grindstone chips on an outer periphery.
In the grinding machining using this grinding wheel, when a workpiece is ground, the grindstone chips are abraded away, and replacement of the grinding wheel is required. Thus, in terms of suppressing an increase in cost, there is a demand to extend a life span of the grinding wheel.